U.S. Geological Survey heavy metals program progress report 1968 -- Field studies

Circular 621




As one means of transporting crude oil from oil fields on the Alaskan Arctic coast to a year-round ice-free port, a large pipeline traversing most of the state of Alaska from north to south has been proposed. Plans call for a pipe 4 feet in diameter, which will be buried along most of the route in permafrost. According to preliminary estimates, the initial heat in the oil plus frictional heating in the pipe are expected to maintain oil temperatures in the neighborhood of 70 ? to 80?C (158 ? to 176?F) along the route when full production is achieved. Such an installation would thaw the surrounding permafrost. Where the ice content of permafrost is not high, and other conditions are favorable, thawing by the buried pipe might cause no special problems. Under adverse local conditions, however, this thawing could have significant effects on the environment, and possibly upon the security of the pipeline. It is important that any potential problem be identified prior to its occurrence so that it can be accommodated by proper pipeline design. Identifying a problem in advance depends upon an understanding of the conditions under which the problem will occur. For that reason much of this report is concerned with problems. If the pipeline system is properly designed, and if it is constructed and maintained in compliance with the design, they will not occur. Perhaps 'proper design' in some areas will involve abandoning plans for burial or changing the route; in others it might involve burying the pipe and invoking special engineering designs or monitoring procedures. These are matters to be determined by much additional study and an intensive program of field and laboratory measurements of conditions along the route. In this report a few basic principles are applied to simplified models of permafrost regimes to identify some effects of a heated pipe, the conditions that control them, and the approximate ranges of physical properties for which these effects are likely to result in problems. The computations are approximate, and the problems discussed are only illustrative examples. Comprehensive discussions of these and related effects, taking account of physical and theoretical refinements, are beyond the scope of the report. Refined studies will probably be needed, however, to form an adequate basis for engineering design. It is difficult to summarize these effects briefly, but a few will be mentioned. The reader is urged to consult the full text for a more complete statement of the-conditions under which they are likely to occur. It should be emphasized that whether or not such conditions exist is a matter yet to be determined by measurements on permafrost materials along the pipeline route. Such measurements are essential for predictions of the interaction between the pipeline and its environment. A 4-foot pipeline buried 6 feet in permafrost and heated to 80?C (176?F) will thaw a cylindrical region 20 to. 30 feet in diameter in a few years in typical permafrost materials. At the end of the second decade of operation, typical thawing depths would be 40 to 50 feet near the southern limit of permafrost and 35 to 40 feet in northern Alaska where permafrost is colder. Except for special materials near the northern end, equilibrium conditions will not be reached and thawing will continue throughout the life of the pipeline, but at a progressively decreasing rate. If the thawed material or the water within it flows, these amounts of thawing can be increased several fold. If the pipeline temperature were only 30?C (instead of 80?C), the depth of thawing would probably be reduced by only 30 or 40 percent. The principal effect of insulating the pipe would be to increase oil temperatures rather than to decrease thawing. If permafrost sediments have excess ice and a very low permeability when thawed, melting below the pipe could generate free water faster than it could filter to the surface. As a result the material in the thawe

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U.S. Geological Survey heavy metals program progress report 1968 -- Field studies
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The Survey,
iii, 35 p. ;26 cm.